Optical surfaces

Optical surfaces

Interfaces between different optical media at which light is refracted or reflected. From a physical point of view, the basic elements of an optical system are such things as lenses and mirrors. However, from a conceptual point of view, the basic elements of an optical system are the refracting or reflecting surfaces of such components. Surfaces are the basic elements of an optical system because they are the elements that affect the light passing through the system. Every wavefront has its curvature changed on passing through each surface so that the final set of wavefronts in the image space may converge on the appropriate image points. Also, the aberrations of the system depend on each surface, the total aberrations of the system being the sum of the aberrations generated at the individual surfaces. See Aberration (optics), Reflection of electromagnetic radiation, Refraction of waves

Optical systems are designed by ray tracing, and refraction at an optical surface separating two media of different refractive index is the fundamental operation in the process. The transfer between two surfaces is along a straight line if, as is usually the case, the optical media are homogeneous. The refraction of the ray at a surface results in a change in the direction of the ray. This change is governed by Snell's law.

The vast majority of optical surfaces are spherical in form. This is so primarily because spherical surfaces are much easier to generate than nonspherical, or aspheric, surfaces. Moreover, lens systems seldom need aspherics because the aberrations can be controlled by changing the shape of the component lenses without changing their function in the system, apart from modifying the aberrations. Also, many lens components can be included in a lens system in order to control the aberrations. See Lens (optics)

On the other hand, mirror systems usually require aspheric surfaces. Unlike lenses, where the shape can be changed to modify the aberrations, mirrors cannot be changed except by introducing aspheric surfaces. Mirror systems are further constrained by the fact that only a few mirrors, usually two, are used in a system because each successive mirror occludes part of the beam going to the mirror preceding it. See Mirror optics

The most common form of rotationally symmetric surface is the conic of revolution. The departure of conic surfaces from spherical form is shown in the illustration. The classical virtue of the conics of revolution for mirrors is the fact that light from a point located at one focus of the conic is perfectly imaged at the other focus. If these conic foci are located on the axis of revolution, the mirror is free of spherical aberration for such conjugate points.

Conics of revolutionenlarge picture
Conics of revolution
References in periodicals archive ?
Researchers have developed a cooling system that involves specialized optical surfaces that can cool flowing water to a temperature below that of the surrounding air.
This would allow the parts to be removed, transported and handled safely through subsequent processes, without the need to touch the critical optical surfaces.
Procured is a device to measure the contact cut and polished optical surfaces, allowing the entire surface to measure spherical, aspherical, but especially toric, cylindrical or freeform surface geometry with a diameter up to 200 mm.
Photonic Cleaning Technologies introduces First Contact Polymer Solutions ($110), which cleans your optical surfaces without leaving residue.
Superabrasives specialist Engis, has developed a new process for polishing Laser grade-quality optical surfaces, which enables materials including: Zinc Selenide, Zinc Sulfide, Germanium, Silicon, Calcium Fluoride and Magnesium Fluoride, to be polished using exactly the same diamond slurry and composite plate combination.
Durham University hosts the project and principle investigator Professor Ray Sharples, of the Department of Physics, who is also the Director of the Centre for Advanced Instrumentation, said: "One of the unique features of KMOS is the system of diamond-machined image slicers, produced by Durham Precision Optics, which consists of over a thousand gold-coated optical surfaces each manufactured with a precision of a few billionths of a metre.
Among specific topics are calculating the effective ground depth of cut by means of a grinding process model, comparing picosecond and femtosecond laser ablation for the surface engraving of metals and semiconductors, pulsed processes when cutting heat-resistant alloys, reactive atom plasma for the rapid figure correction of optical surfaces, and the thrust force of printed circuit board drilling.
Additionally, and perhaps more importantly, the TIR approach provides two additional refractive optical surfaces which can be used to shape the light distribution emanating from the LED.
The mirrors were rinsed thoroughly with distilled water before wads of cotton wool soaked in a weak sodium lauryl sulphate solution were used to drag-wipe the optical surfaces.
We would also like to hear from anyone who may be able to help with the acquisition of a suitable 2-mirror type coelostat delivering a beam between 4 and 12 inches clear aperture: it doesn't matter how old and well-worn, as long as the optical surfaces are undamaged and the mechanicals serviceable.
The lens is constructed with two flexible membranes on the optical surfaces, held in place by a solid surround.

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